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Potential Invasive Plant Establishment After Dam Removal: A Case Study of the Elwha River Dams Trevor Sheffels November 25, 2009 Outline • Background – Dam removal in the United States – Invasive plant establishment • Research on invasions after dam removal • Case Study – History of the Elwha River – Potential invasive plant establishment Outline • Background – Dam removal in the United States – Invasive plant establishment • Research on invasions after dam removal • Case Study – History of the Elwha River – Potential invasive plant establishment Dam Removal in the United States • Majority of dams are nearing end of licensing agreements • Approximately 500 dams have been removed in the last decade • Pacific Northwest is prominent in dam removal discussions due to salmon migration issues Importance to Limnology • Conversion from manmade lentic reservoirs to natural lotic rivers • Dam removal completely alters watershed biogeochemical processes • Large-scale disturbance that results in variety of ecosystem impacts Invasive Plant Establishment • Invasive species are often found in disturbed habitats (Elton 1958) • Invasive plants are often pioneer species • Life history strategies allow invasive plants to outcompete native species Outline • Background – Dam removal in the United States – Invasive plant establishment • Research on invasions after dam removal • Case Study – History of the Elwha River – Potential invasive plant establishment Invasions After Dam Removal • Resident seed bank can contain viable invasive species seeds (Nishihiro and Washitani 2007) DAM REMOVAL • Natural revegetation of exposed reservoir can be prone to invasive species (Auble et al. 2007) • Natural hydrology results in new source of invasive species introduction downstream (Gurnell et al. 2006) Exposed seed bank Lake bed colonization Downstream transport Outline • Background – Dam removal in the United States – Invasive plant establishment • Research on invasions after dam removal • Case Study – History of the Elwha River – Potential invasive plant establishment Elwha River Dams • Watershed covers 20% of Olympic National Park • Two hydroelectric dams constructed in early 1900s • Native salmon habitat has been severely restricted Glines Canyon and Elwha Dams • Glines Canyon Dam – 210 feet tall – Lake Mills reservoir covers 415 acres • Elwha Dam – 108 feet tall – Lake Aldwell reservoir covers 267 acres Reservoir Bed Seed Banks • Seed bank is trapped mostly in fine sediment • 50% of Lake Mills seed bank is viable (Brown and Chenoweth 2008) • 15% of these seeds are invasive species (Brown and Chenoweth 2008) Exposed Sediment • 18 million cubic yards of accumulated sediment in two reservoirs (Mussman et al. 2008) • 13 invasive species are present and likely to establish (Brown unpublished) • Initial establishment could result in long-term problems (Orr and Stanley 2006) Invasive Species Downstream • Large quantity of sediment will move downstream over short period of time (Mussman et al. 2008) • Natural levels of hydrochory will be restored (Brown and Chenoweth 2008) • Establishment of natural stream banks may be an issue Conclusions • Invasive species establishment should be considered when considering tradeoffs of dam removal • Processes are not well-understood and further research is needed • Elwha project provides a unique opportunity to study invasive species establishment following a large dam removal References Auble, G.T., P.B. Shafroth, M. Scott, and J.E. Roelle. 2007. Early vegetation development on an exposed reservoir: implications for dam removal. Journal of Environmental Management 39: 806-818. Brown, R.L. and J. Chenoweth. 2008. The effect of Glines Canyon Dam on hydrochorous seed dispersal in the Elwha River. Northwest Science 82: 197-209. Elton, Charles. 1958. The ecology of invasions by animals and plants. Methuen, London, England. Gurnell, A.M., A.J. Boitsidis, K. Thompson, and N.J. Clifford. 2006. Seed bank, seed dispersal and vegetation cover: colonization along a newly-created river channel. Journal of Vegetation Science 17: 665–674. Mussman, E.K., D. Zabowski, and S.A. Acker. 2008. Predicting secondary reservoir sediment erosion and stabilization following dam removal. Northwest Science 82: 236-246. Nishihiro J. and I. Washitani. 2007. Restoration of lakeshore vegetation using sediment seed banks: studies and practices in Lake Kasumigaura, Japan. Global Environmental Research 11: 171-177. Orr, C.H. and E.H. Stanley. 2006. Vegetation development and restoration potential of drained reservoirs following dam removal in Wisconsin. River Research and Applications 22:281-295.